The prior art already discloses processes and apparatuses making it possible to produce such electrolytic metal deposits on weakly conductive substrates.
Japanese patent application JP-60-228697 of Nov. 13, 1985 describes an apparatus making it possible to metallize semiconductor substrates. The substrate is placed at the upper opening of an electrolytic deposition cell. Its rear face is in contact with a planar electrode, which closes the cell and forms the cathode. The anode is placed in the electrolytic deposition cell and faces said substrate. The application of an electric current to the two terminals of the electrodes makes it possible to produce the deposit.
This apparatus suffers from the disadvantage of only being useable with a rigid substrate in order that its rear face is kept in contact with the planar cathode and can rest on the edge or ledge of the electrolytic deposition cell. This apparatus also does not make it possible to produce deposits of varying shapes, e.g., by leaving part of the substrate uncoated. Finally, semicontinuous deposits cannot be produced with this apparatus, because it is necessary to dismantle the cathode at the end of each deposition process in order to remove the coated substrate and put a new substrate into place.
French patent application FR-A-2 649 126 of Jun. 30 1989, describes a process for metallic electrochemical deposition on an electrically insulating material. As the substrate to be coated is insulating, prior to the metal deposition, it must be rendered conductive by the deposition on its surface of an electronically conductive polymer. It is then scarcely immersed in a solution of a salt of the metal to be deposited. A high voltage of several dozen volts is applied between the pretreated substrate serving as the cathode and an anode immersed in the electrolytic solution. If deposition takes place at the end of the substrate, the latter is gradually introduced into the solution, at the same time as the voltage applied is reduced. Finally, the substrate is kept at a voltage of a few volts for 30 to 45 minutes until a satisfactory deposit is obtained.
This process suffers from the disadvantage of being extremely slow and only permitting randomly shaped metal deposits by using a complex mask system. Thus, these two disadvantages render impossible a semicontinuous, rapid deposition.
Finally, US-A-3 723 283 (Johnson) discloses an electrodeposition apparatus making it possible to produce deposits having a specific shape on a material strip or fabric. The fabric is unrolled semi-continuously in front of several successive working stations, where it undergoes several treatments. This apparatus comprises two mobile deposition heads, which can move towards or away from one another in order to grip the fabric on which the deposition is made. The electrolyte to be deposited is passed through these deposition heads. However, if it is wished to modify the shape of the deposit made, the complete deposition head must be changed.